Expandable and adjustable lordosis interbody fusion system

ABSTRACT

A spinal implant device for placement between vertebral bodies includes a housing, at least one screw member in the housing, and at least one drive shaft operably engageable with the screw member. The housing includes a first shell member and a second shell member. At least the first shell member has step tracking comprising a plurality of individual riser members for receiving the at least one screw member. The height of the plurality of individual riser members may change along the step tracking. The drive shaft may be operable to rotate the at least one screw member, causing the at least one screw member to move on the plurality of individual riser members. The at least one screw member comprises an external helical thread having a thickness configured to fit in the gaps between adjacent individual riser members, and is engageable with the first and second shell members, whereby the first and second shell members move relative to each other in response to the rotation of the at least one screw member to effect an expansion of the housing or a contraction of the housing from the expansion by reversing the rotation of the at least one screw member.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.16/001,852 filed Jun. 6, 2018 entitled “EXPANDABLE AND ADJUSTABLELORDOSIS INTERBODY FUSION SYSTEM,” which is a continuation of U.S.application Ser. No. 15/859,241 filed Dec. 29, 2017 entitled “EXPANDABLEAND ADJUSTABLE LORDOSIS INTERBODY FUSION SYSTEM,” issued as U.S. Pat.No. 10,188,527 on Jan. 29, 2019, which is a continuation of Ser. No.14/473,200 filed Aug. 29, 2014 entitled “EXPANDABLE AND ADJUSTABLELORDOSIS INTERBODY FUSION SYSTEM,” issued as U.S. Pat. No. 9,889,019 onFeb. 13, 2018, which claims priority to U.S. provisional patentapplication No. 61/871,780 filed Aug. 29, 2013 entitled “EXPANDABLELATERAL INTERBODY FUSION SYSTEM,” the disclosures of all of which arehereby incorporated by reference in their entirety.

This application claims priority to U.S. provisional patent applicationNo. 62/736,649 filed Sep. 26, 2018 entitled “EXPANDABLE AND ADJUSTABLELORDOSIS INTERBODY FUSION SYSTEM,” the disclosures of all of which arehereby incorporated by reference in their entirety.

TECHNICAL FIELD

The invention relates to surgical procedures and apparatus for treatinglumbar back pain.

BACKGROUND OF THE INVENTION

Lumbar spinal fusion is a surgical procedure to correct problemsrelating to the human spine. It generally involves removing damaged discand bone from between two vertebrae and inserting bone graft materialthat promotes bone growth. As the bone grows, the two vertebrae join, orfuse, together. Fusing the bones together can help make that particulararea of the back more stable and help reduce problems related to nerveirritation at the site of the fusion. Fusions can be done at one or moresegments of the spine.

Interbody fusion is a common procedure to remove the nucleus pulposusand or the annulus fibrosus that compose the intervertebral disc at thepoint of the back problem and replace it with a cage configured in shapeand dimension to restore the distance between adjacent vertebrae to thatof a proper condition. Surgical approaches to implement interbody fusionvary, and access to the patient's vertebral column can be made throughthe abdomen or back. One other surgical method for accomplishing lumbarspinal fusion in a less invasive way involves accessing the vertebralcolumn through a small incision on the side of the body. This procedureis known as lateral lumbar interbody fusion.

Once the intervertebral disc is removed from the body during the laterallumbar interbody fusion, the surgeon typically forces different trialimplants between the vertebral endplates of the specific region todetermine the appropriate size of the implant for maintaining a distancebetween the adjacent vertebrae. Another consideration is to maintain thenatural angle between lumbar vertebral bodies to accommodate thelordosis, or natural curvature, of the spine. Therefore, duringselection of a cage for implantation, both intervertebral disc heightand lordosis must be considered. Prior art fusion cages are oftenpre-configured to have top and bottom surfaces angles to one another toaccommodate the natural curvature of the spine. It is unlikely thatthese values can be determined precisely prior to the operation, whichis a drawback in present procedures. Prepared bone graft is generallypacked into the cage implant once it is properly sized and before it isinserted in between the vertebral bodies.

Present lateral interbody fusion cage devices are generally limited toproviding height expansion functions, but not a lordotic adjustmentcapability. In implementing a trial-and-error approach to sizing andfitting the interbody fusion cage into the target region for theparticular geometric configuration for that patient, the patient issubjected to significant invasive activity. The bone graft material isgenerally added and packed in to the fusion device after the desiredheight expansion has been reached and final adjustments made.

SUMMARY OF THE INVENTION

An embodiment of the device comprises an expandable housing comprised ofopposing shell members. Movable tapered screw-like elements having anexternal helical thread are disposed in the housing and operably engageagainst the top and bottom shell members, urging them apart to causeexpansion in the height of the housing. This function permits adjustmentof the distance (height) between adjacent vertebrae when in place. Thetapered members are disposed in a dual arrangement such that independentengagement of the tapered members along lateral portions of the top andbottom shells cause an angular tilt to the exterior surface of thehousing when the wedge Members are moved to different degrees. Thisfunction permits adjustment in the angular relationship between adjacentvertebrae and assists the lordotic adjustment of the patient's spine.When the functions of the device are used in combination by the surgeon,the device provides an effective tool for in situ adjustment whenperforming lateral lumbar interbody fusion.

An embodiment of the device further comprises a track configurationwithin the housing for guiding the tapered external helical threadedmembers in their engagement with the top and bottom shell members. Thetrack comprises raised elements on each of the interior surfaces of thetop and bottom shell members that permit an interlocking engagement forlateral stability of the housing when in a contracted position. As thehousing expands, the track area provides space for storage of bone graftmaterial. One embodiment may provide for an elastic membrane to bepositioned around the housing to prevent bone graft material fromseeping out of the cage and to provide a compressive force around thecage to provide structural stability to the housing

An embodiment of the device further comprises drive shafts for operatingthe tapered external helical threaded members. The drive shafts permitthe surgeon, through the use of a supplemental tool, to manipulate theshafts which operatively move the tapered external helical threadedmembers in controlling the expansion of the housing and angularadjustment of the top and bottom shell members for in situ fitting ofthe interbody fusion device. A locking mechanism is provided forpreventing rotation of the shafts when the tool is not engaged and aftermanipulation by the tool is completed. The tool also facilitatesinsertion of bone graft material into the fusion body during in situadjustment.

An embodiment of the present invention provides a surgeon with theability to both expand the fusion cage and adjust the lordotic angle ofthe fusion cage in situ during operation on a patient and to introducebone graft material at the operation site while the device is in place.This embodiment of the present invention therefore provides a fusioncage having geometric variability to accommodate the spinal conditionunique to each patient.

Embodiments of the present invention therefore provide an interbody cagedevice for use in lateral lumbar interbody fusion procedures thatcombines the functions of height expansion for adjusting the distancebetween adjacent vertebrae with lordotic adjustment to control theangular relationship between the vertebrae. Embodiments of the inventiveinterbody cage device further provide a storage capacity for containingbone graft material in the interbody cage device as disc height andlordotic adjustment takes place in situ.

The present invention also provides a device that may be used inenvironments other than in interbody fusion applications. It maygenerally be used to impart a separating effect between adjacentelements and to impart a variable angular relationship between theelements to which it is applied.

An embodiment of a spinal implant device for placement between vertebralbodies includes a housing, at least one screw member in the housing, andat least one drive shaft operably engageable with the screw member. Thehousing includes a first shell member and a second shell member. Atleast the first shell member has step tracking comprising a plurality ofindividual riser members for receiving the at least one screw member.The height of the plurality of individual riser members may change alongthe step tracking. The drive shaft may be operable to rotate the atleast one screw member, causing the at least one screw member to move onthe plurality of individual riser members. The at least one screw membercomprises an external helical thread having a thickness configured tofit in the gaps between adjacent individual riser members, and isengageable with the first and second shell members, whereby the firstand second shell members move relative to each other in response to therotation of the at least one screw member to effect an expansion of thehousing or a contraction of the housing from the expansion by reversingthe rotation of the at least one screw member.

An embodiment of a spinal implant device comprises a housing, a firstpair of screw members and a second pair of screw members in the housing,a first drive shaft operably engageable with the first pair of screwmembers and a second drive shaft operably engageable with the secondpair of screw members. The housing comprises a first shell member and asecond shell member each having a plurality of individual riser members.The plurality of individual riser members of the first and second shellmembers define a first step tracking run along a first lateral area ofthe housing and a second step tracking run along a second lateral areaof the housing. The height of the plurality of individual riser memberschange along the first and second step tracking runs. The first driveshaft is operable to rotate the first pair of screw members causing thefirst pair of screw members to move along the first step tracking run.The second drive shaft is operable to rotate the second pair of screwmembers causing the second pair of screw members to move along thesecond step tracking run. The first and second drive shafts are operableindependently of each other. The first and second pairs of screw memberseach comprises an external helical thread having a thickness configuredto fit in a gap between adjacent individual riser members and isengageable with the first and second shell members, whereby the firstand second shell members move relative to each other in response torotation of the first and/or second pairs of screw members to effect anexpansion of the housing or a contraction of the housing from theexpansion by reversing the rotation of the first and/or second pairs ofscrew members, wherein a degree of expansion or contraction of the firstlateral area of the housing is independently adjustable relative to adegree of expansion or contraction of the second lateral area of thehousing when the first and second pairs of screw members are rotatedindependently to different positions on the first and second steptracking runs.

These and other features of the present invention are described ingreater detail below in the section titled DETAILED DESCRIPTION OF THEINVENTION.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURES

An embodiment of the present invention is described herein withreference to the following drawing figures, with greater emphasis beingplaced on clarity rather than scale:

FIG. 1 is a view in side elevation from the side of the expandable shelldevice.

FIG. 2 is a perspective view of a bottom section of the expandableshell.

FIG. 3 is a top plan view of the bottom section of the expandable shell.

FIG. 4 is a top plan view of the expandable shell device.

FIG. 5 is a perspective view of a tapered external helical threadedmember.

FIG. 5A is a view in side elevation from the side of the taperedexternal helical threaded member.

FIG. 5B is a view in side elevation from the front of the taperedexternal helical threaded member.

FIG. 6 is a cross-sectional view of the device taken along lines 6-6 inFIG. 1.

FIGS. 7A-7C are a series of views in side elevation of the device as itundergoes expansion.

FIG. 8 is a view in side elevation of the device showing an expansion ofthe device to accommodate a lordotic effect.

FIG. 9A is a perspective expanded view of thrust bearing for the driveshaft.

FIG. 9B is a perspective view of the drive shafts and thrust bearings.

FIG. 9C is a top plan view in cross section of the area of engagement ofthe drive shafts with the thrust bearings.

FIG. 10 is a side elevation view of the housing as expanded.

FIG. 11A is a top plan view of another embodiment of the device.

FIG. 11B is a top plan view of yet another embodiment of the device.

FIG. 12A is a top plan view of the drive shafts disengaged by thelocking mechanism.

FIG. 12B is a top plan view of the drive shafts engaged by the lockingmechanism.

FIG. 13A is a perspective view of the locking mechanism.

FIG. 13B is a top plan cross sectional view of the drive shaftsdisengaged by the locking mechanism.

FIG. 13C is a top plan cross sectional view of the drive shafts engagedby the locking mechanism.

FIG. 14 is a view taken along lines 14-14 in FIG. 11A.

FIGS. 15A-C are a series of views in side elevation taken from the endof the device as it undergoes expansion showing the lordotic effect.

FIG. 16 is a perspective view of the operating tool.

FIG. 17 is a view showing a manner of attachment of the operating toolto the drive shafts of the device.

FIG. 18 is a breakaway perspective view of the handle of the operatingtool.

FIG. 19 is a perspective view of gears in the handle engaged foroperation of both drive shafts.

FIG. 20 is a perspective view of gears in the handle disengaged foroperation of a single drive shaft.

FIG. 21 is a perspective top view of an exemplary spinal implant deviceaccording to embodiments of the disclosure.

FIG. 22 is a cross-sectional view of an exemplary spinal implant deviceaccording to embodiments of the disclosure.

FIG. 23 is a perspective side view of an exemplary spinal implant deviceaccording to embodiments of the disclosure.

FIG. 24 is a cutaway, front view of an exemplary spinal implant deviceaccording to embodiments of the disclosure.

FIG. 25 schematically shows a tapered screw member according toembodiments of the disclosure.

FIG. 26 schematically shows a tapered screw member engaging individualriser members according to embodiments of the disclosure.

FIG. 27 is an exploded view of a thrust bearing member according toembodiments of the disclosure.

FIG. 28 is a cutaway view of a thrust bearing member in relation toother components of an exemplary spinal implant device according toembodiments of the disclosure.

FIG. 29 is cutaway view of a thrust bearing member in relation to othercomponents of an exemplary spinal implant device according toembodiments of the disclosure.

FIG. 30 is a perspective view of an exemplary spinal implant device in aparallel configuration according to embodiments of the disclosure.

FIG. 31 is a perspective view of an exemplary spinal implant device in alordosis configuration according to embodiments of the disclosure

DETAILED DESCRIPTION OF THE INVENTION

With reference to the drawings, an interbody fusion body device isherein described, shown, and otherwise disclosed in accordance withvarious embodiments, including preferred embodiments, of the presentinvention. The interbody fusion device 10 is shown generally in FIG. 1.It is comprised of a housing 12 having a top shell 14 and a bottom shell16. The overall housing may have a length of 50 mm and a width of 20 mm,as an example. The shell material may be comprised of a suitablematerial, such as titanium alloy (Ti-6AL-4V), cobalt chromium, orpolyether ether ketone (PEEK). Other materials may be suitable that canprovide sufficient compositional integrity and that have suitablebiocompatible qualities. The interior of the shells is configured with acascading step tracking 18 and 20 placed along their lateral edges. Asshown in FIG. 2, step tracking 18 begins towards the midpoint of aninner surface of bottom shell 16 with successive track steps increasingin height as the tracking extends to a first end of bottom shell 16.Correspondingly, step-tracking 20 begins towards the midpoint of theinner surface of bottom shell 16 with successive track steps increasingin height as that portion of the tracking extends to a second oppositeend of bottom shell 16. Step tracking 18 comprises dual track runs 22and 24 while step tracking 20 comprises dual track runs 26 and 28 asshown in FIG. 3. Corresponding step tracking 30 and 32 is provided ontop shell 14 as shown in FIG. 4. When the device is in its fullycompressed state where top shell 14 lies adjacent to bottom shell 16, asshown in FIG. 1, step tracking 18 intermeshes with step tracking 30 andstep tracking 20 intermeshes with step tracking 32.

The respective track runs comprise a series of risers, or track steps,which are spaced apart to receive the threads of tapered externalhelical threaded members. The tapered external helical threaded membersprovide a wedging action for separating the top and bottom shell therebyincreasing the height of the housing to effect expansion between thevertebral bodies in which the device is placed. As shown in FIG. 4,track run 22 receives tapered external helical threaded member 34, trackrun 24 receives tapered external helical threaded member 36, track run26 receives tapered external helical threaded member 38, and track run28 receives tapered external helical threaded member 40. Track run 22aligns collinearly with track run 26 such that the travel of taperedexternal helical threaded members 34 and 38 within the respective trackruns occurs within that collinear alignment. The thread orientation oftapered external helical threaded members 34 and 38 are opposite of eachother such that their rotation will result in opposite directionalmovement with respect to each other. As shown in FIG. 4, a drive shaft42 runs along the collinear span of track runs 22 and 26 and passesthrough tapered external helical threaded members 34 and 38. Shaft 42has a square cross-sectional configuration for engaging and turning thetapered external helical threaded members. As shown in FIG. 5, thecentral axial opening 44 of the tapered external helical threadedmembers are configured to receive and engage the shaft 42. Shaft 42 mayalternatively comprise any shape for effectively creating a spline, suchas a hexagonal shape, and central axial openings 44 may comprise acorresponding configuration for receiving that shape. As shaft 42 isrotated by its end 48 in a clockwise direction, tapered external helicalthreaded members 34 and 38 are rotated and their respective threadorientations cause the screws to travel apart from each other alongtrack run 22 and track run 26, respectively. Correspondingly, as shaft42 is rotated by its end 48 in a counter-clockwise direction, taperedexternal helical threaded members 34 and 38 are caused to travel towardseach other along track run 22 and track run 26, respectively.

Similarly, track run 24 aligns collinearly with track run 28 such thatthe travel of tapered external helical threaded members 36 and 40 withinthe respective track runs occurs within that collinear alignment. Thethread orientation of tapered external helical threaded members 36 and40 are opposite of each other such that their rotation will result inopposite directional movement with respect to each other. Also, shaft 46passes through and engages tapered external helical threaded members 36and 40. However, the orientation of tapered external helical threadedmembers 36 and 40 is reversed from the orientation of tapered externalhelical threaded members 34 and 38. Under this orientation, as shaft 46is rotated by its end 50 in a counter-clockwise direction, taperedexternal helical threaded members 36 and 40 are rotated and theirrespective thread orientations cause the screws to travel apart fromeach other along track run 24 and track run 28, respectively.Correspondingly, as shaft 46 is rotated by its end 50 in a clockwisedirection, tapered external helical threaded members 36 and 40 arecaused to travel towards each other along track run 24 and track run 28,respectively.

As shown in FIG. 2, the step tracking is configured with a cascadingseries of risers of increasing height. For example, each track run hasrisers 52-60 as shown for step tracking 18 in FIG. 2. As the thread of atapered external helical threaded member travels into the gap betweenriser 52 and 54, the positional height of the tapered external helicalthreaded member body, as supported on risers 52 and 54, increases withinthe housing 12. As the tapered external helical threaded membercontinues to travel along the track run, its thread passes from the gapbetween risers 52 and 54 and enters the gap between risers 54 and 56which raises the tapered external helical threaded member body furtherwithin housing 12 as it is supported on risers 54 and 56. As the taperedexternal helical threaded member continues its travel along theremainder of the step risers 58 and 60 its positional height increasesfurther. As the positional height of the tapered external helicalthreaded member body increases, it urges top shell 14 apart from bottomshell 16 as shown in the series of FIGS. 7A-7C.

The combined effect of rotating the tapered external helical threadedmembers to cause their movement towards the outer ends of the respectivetrack runs causes an expansion of the housing 12 as shown in FIG. 7. Thefully expanded shell is shown in FIG. 10. The housing 12 may becontracted by reversing the movement of the tapered external helicalthreaded members such that they travel back along their respective trackruns towards the midpoint of the housing. The housing will optimallyprovide expansion and contraction to give the implant device a heightover a range of around approximately 7.8 mm to 16.15 mm in the presentembodiment. The device of this embodiment of the invention can beadapted to provide different expansion dimensions.

The pairs of tapered external helical threaded members in each collineardual track run may be rotated independently of the pair of taperedexternal helical threaded members in the parallel track run. In thisarrangement, the degree of expansion of that portion of the housing overeach collinear track run may be varied to adjust the lordotic effect ofthe device. As an example shown in FIG. 8, tapered external helicalthreaded members 36 and 40 have been extended to a particular distancealong track run 24 and track run 28, respectively, causing the top shell14 to separate from bottom shell 16 thereby expanding housing 12.Tapered external helical threaded members 34 and 38 have been extendedto a lesser distance along parallel track run 22 and 26, respectively,causing that portion of the top shell over track runs 22 and 26 toseparate from bottom shell to a lesser degree. The series of FIGS.15A-15C show this effect where tapered external helical threaded members36 and 40 are extended apart from each other in further increasingincrements where the tapered external helical threaded members 34 and 38maintain the same relative distance to each other.

In FIG. 15A, the respective positioning of the set of tapered externalhelical threaded members 36-40 is approximately the same as the set oftapered external helical threaded members 34-38 in their respectivetracking. In this position, the top shell 14 is essentially parallelwith bottom shell 16. In FIG. 15B, the set of tapered external helicalthreaded members 36-40 move further distally apart along their trackingas the set of tapered external helical threaded members 34-38 remains attheir same position in FIG. 15A. In this setting, the lateral edge oftop shell 14 along which tapered external helical threaded members 36and 40 travel is moved higher with respect to the lateral edge of topshell 14 along which tapered external helical threaded members 34 and 38travel, giving a tilt to top shell 14 with respect to bottom shell 16.In FIG. 15C, the set of tapered external helical threaded members 36-40move even further distally apart along their tracking with respect tothat of the set of tapered external helical threaded members 34-38,giving an even greater tilt to top shell 14 with respect to bottom shell16. Through the independent movement of the respective tapered externalhelical threaded member sets, the device can achieve a lordotic effectof between 0° and 35° in the present embodiment. The device of thisembodiment of the invention can be adapted to provide different lordotictilt dimensions.

The tapered external helical threaded members have a configurationcomprising a body profile that has an increasing minor diameter fromD_(r1) to D_(r2) as shown in FIG. 5. The threads 33 have a pitch tomatch the spacing between the riser elements 52-60 in the tracking runsas shown in FIG. 4. Threads 33 can have a square profile to match theconfiguration between the risers, but other thread shapes can be used asappropriate. The increasing diameter and tapering aspect of the helicalthreaded members cause top shell 14 and bottom shell 16 to move apart asdescribed above. The contact at the tops of the risers 52-60 is made atthe minor diameter of the helical threaded member.

Thrust bearings are provided to limit the axial direction motion of thedrive shafts within shell 12. As shown in FIG. 9A, thrust bearing 62comprises a two-piece yoke configuration that mate together andpress-fit around ends of the shafts. The top part 64 of the thrustbearing yoke defines openings for receiving a round portion 66 of theshaft ends. In FIG. 9C, square shaft 42 has a rounded portion 66 oflesser diameter than the square portion of the shaft. A mating piece 65of the thrust bearing engages with top part 64 to encircle the roundedportion 66 of drive shaft 42.

Pin elements 68 in the top portion 64 and bottom portion 65 engages acorresponding hole 69 in the mating piece to provide a press fit of thethrust bearing around the shaft. Journal grooves 67 can also be providedin thrust bearing 62. Shaft 42 can have an annular ridge 63 around itsrounded portion 66 which is received in journal groove 67 as shown inFIG. 9C. A thrust bearing is provided at each end of the drive shafts asshown in FIG. 9B. As shown in FIG. 6, the thrust bearings restrict theaxial movement of the drive shafts in the housing.

A safety lock is provided at the proximal end of the device forpreventing unintended rotation of the shafts. As shown in FIGS. 12A and12B, safety lock member 70 is provided for engagement with the proximalends of drive shafts 42 and 46. The openings 73 in safety lock member 70are configured with the shape of the cross-sectional configuration ofthe drive shafts (see FIG. 13A). A portion of the drive shafts has anarrowed, rounded configuration 71 such that the drive shaft can rotatefreely while the rounded portion of the shaft is in alignment with thesafety lock member openings 73 (see FIG. 13C). FIG. 12B shows thisrelationship among the safety lock member 70, thrust bearing 62 anddrive shafts 42 and 46. When the non-narrowed portions 75 of the shaftsare placed in alignment with the safety lock member openings 73, thenrotation of the shafts is prevented (see FIG. 13B). FIG. 12A shows thisrelationship among the safety lock member 70, thrust bearing 62 anddrive shafts 42 and 46. A compression spring 77 can be placed betweenthrust bearing 62 and safety lock member 70 to urge safety lock memberback over the square portion 75 of the drive shafts. FIG. 12B shows alock disengagement when the safety lock member 70 is pushed forward outof alignment with the square portions 75 and placed in alignment withthe rounded portions 71 of shafts 42 and 46. Post 79 can be disposedbetween safety lock member 70 and thrust bearing 62 on which compressionspring 77 can be positioned. Post 79 can be fixedly connected to safetylock member 70 and an opening can be provided in thrust bearing 62through which post 79 can slide. Post 79 is provided with head 81 tolimit the backward movement of safety lock member 70 from thecompressive force of spring 77.

The interaction of the tapered external helical threaded members withthe step tracking contributes to self-locking under a power screwtheory. In considering the variables for promoting a self-locking aspectof the tapered threaded members, certain factors are relevant. Inparticular, those factors include the coefficient of friction of thematerials used, such as Ti-6Al-4V grade 5, the length of pitch of thehelical threads and the mean diameter of the tapered member. Thefollowing equation explains the relationship among these factors indetermining whether the tapered external helical threaded members canself-lock as it travels along the step tracking:

$T_{R} = {\frac{{Fd}_{m}}{2}\left( \frac{l + {\pi\;{fd}_{m}\sec\;\alpha}}{{\pi\; d_{m}} - {{fl}\mspace{14mu}\sec\;\alpha}} \right)}$

The above equation determines the torque necessary to apply to the driveshafts engaging the tapered external helical threaded members forexpanding the shell members. This torque is dependent upon the meandiameter of the tapered external helical threaded members, the load (F)applied by the adjacent vertebral bodies, the coefficient of friction(f) of the working material, and the lead (l) or, in this embodiment,the pitch of the helical threading. All of these factors determine therequired operating torque to transform rotational motion into a linearlift to separate the shell members in accomplishing expansion andlordosis.

The following equation describes the relationship among the factorsrelating to the torque required to reverse the tapered external helicalthreaded members back down the tracking:

$T_{R} = {\frac{{Fd}_{m}}{2}\left( \frac{{\pi\;{fd}_{m}} - l}{{\pi\; d_{m}} + {fl}} \right)}$

Under this equation, the torque required to lower the tapered externalhelical threaded members (T_(L)) must be a positive value. When thevalue of (T_(L)) is zero or positive, self-locking of the taperedexternal helical threaded members within the step tracking is achieved.If the value of (T_(L)) falls to a negative value, the tapered externalhelical threaded members are no longer self-locking within the steptracking. The factors that can contribute to a failure to self-lockinclude the compressive load from the vertebral bodies, the pitch andmean diameter of the helical thread not being adequately great, and aninsufficient coefficient of friction of the material. The condition forself-locking is shown below:πfd _(m) >I

Under this condition, it is necessary to select an appropriatecombination of sufficient mean diameter size of the tapered member,along with the product material being a greater multiple than the leador pitch in this particular application so that the tapered members canbe self-locking within the step tracking. Based upon average values witha patient lying on their side, the lumbar vertebral body cross sectionalarea is around 2239 mm² and the axial compressive force at that area is86.35 N. With the working material selected to be Ti-6Al-4V, theoperating torque to expand shell housing 12 between L4-L5 of thevertebral column is around 1.312 lb-in (0.148 N-m), and the operatingtorque to contract shell housing 12 between L4-L5 of the vertebralcolumn is around 0.264 lb-in (0.029 N-m).

Alternate embodiments of the expandable shell housing provide fordifferent surgical approaches. FIG. 11A shows housing 100 for use wherea surgeon approaches the lumbar area from an anterior aspect of thepatient. The general configuration of the tracking runs for thisembodiment is similar to that for device 10, but the drive shafts formoving the tapered external helical threaded members are applied with atorque delivered from a perpendicular approach. For this, a dual set ofworm gears 102 and 104 respectively transfer torque to drive shafts 106and 108 as shown in FIG. 14.

FIG. 11B shows housing 200 for use where a surgeon approaches the lumbararea from a transforaminal aspect of the patient. The generalconfiguration of the tracking runs for this embodiment is also similarto that for device 10, but the torque is applied to the drive shaftsfrom an offset approach. For this, a dual set of bevel gears (not shown)may be used to transfer torque to drive shafts 206 and 208.

Housing 12 is provided with numerous niches and open areas in itssurface and interior regions to accommodate the storage of bone graftingmaterial. The interstitial spaces between the risers of the cascadingstep tracking also offers areas for receiving bone-grafting material. Amembrane can be provided as a supplement around housing 12 to helpmaintain compression on the top and bottom shells and to hold in bonegrafting material. Tension spring elements 78 can be provided to holdtogether top member 14 and bottom member 16 as shown in FIG. 10. Theseelements may also serve to provide an initial tension force in thedirection opposite of the expansion against the interbody fusion device.This allows the tapered external helical threaded members to climb therisers in the event that contact between the outer shells and thevertebral bodies is not yet made.

Accordingly, this embodiment of the interbody fusion device of theinstant invention is capable of expansion to provide support betweenvertebral bodies and accommodate the load placed on that region.Furthermore, the inventive interbody fusion device is capable ofachieving a configuration that can provide an appropriate lordotic tiltto the affected region. The device, therefore, provides a significantimprovement with regards to patient-specific disc height adjustment.

The device is provided with a tool for operating the interbody fusiondevice as it is adjusted in situ in a patient's spine. The operatingtool 300 is shown generally in FIG. 16 and comprises a handle member302, a gear housing 304 and torque rod members 306 and 308. The torquerod members connect to the drive shafts of expandable shell 12. Oneembodiment for connecting the torque rod members to the drive shafts ofexpandable shell 12 is shown in FIG. 17. In this arrangement, ends 48and 50 of drive shafts 42 and 46 can be provided with a hex-shaped head.The ends of torque rod members 306 and 308 can be provided withcorrespondingly shaped receivers for clamping around ends 48 and 50.

Within the gear housing 304, handle member 302 directly drives torquerod member 308. Torque rod member 308 is provided with spur gear member310 and torque rod member 306 is provided with spur gear member 312.Spur gear 312 is slidably received on torque rod member 306 and can movein and out of engagement with spur gear 310. Spur gear lever 314 engageswith spur gear 312 for moving spur gear 312 into and out of engagementwith spur gear 310. When torque rod member 308 is rotated by handle 302,and spur gear 312 is engaged with spur gear 310, rotation is translatedto torque rod member 306. In this condition, torque rod member 308rotates drive shaft 46 simultaneously with torque rod member 306 rotatesdrive shaft 42 to effect expansion of shell 12 as shown in FIGS. 7A-7C.Spur gear 312 can be moved out of engagement with spur gear 310 byretracting spur gear lever 314 as shown in FIG. 20. With spur gear 312out of engagement with spur gear 310, rotation of handle 302 only turnstorque rod member 308. In this condition, torque rod member 308 rotatesdrive shaft 46 solely and drive shaft 42 remains inactive to effect thetilt to the top member of shell 12 as shown in FIG. 8 and FIGS. 15A-15Cto achieve lordosis.

To achieve expansion of the device in the described embodiment, theoperator will turn handle member 302 clockwise to engage torqueing. Thisapplied torque will then engage the compound reverted spur gear traincomposed of spur gear members 310 and 312. This series of gears willthen spin torque rod members 306 and 308 in opposite directions of eachother. Torque rod member 308 (in alignment with handle member 302) willspin clockwise (to the right) and torque rod member 306 will spincounterclockwise (to the left). The torque rod members will then rotatethe drive shafts of interbody fusion device 12 expanding it to thedesired height.

To achieve lordosis the operator will move the spur gear lever 314 backtowards handle member 302. By doing so spur gear 312 connected to torquerod member 306 is disengaged from the overall gear train, which in turnwill disengage torque rod member 306. As a result, torque rod member 308will be the only one engaged with the interbody fusion device 12. Thiswill allow the operator to contract the posterior side of the implantdevice to create the desired degree of lordosis.

Referring now to FIGS. 21-29, various embodiments of a spinal implantdevice according to the disclosure will now be described.

FIG. 21 is a perspective top view of an exemplary spinal implant device400 according to embodiments of the disclosure. FIG. 22 is across-sectional view of the spinal implant device 400. FIG. 23 is aperspective side view of the spinal implant device 400. FIG. 24 is acutaway, front view of the spinal implant device 400. As shown in FIGS.21-24, the exemplary spinal implant device 400 includes an expandablehousing 402, a first pair of screw members 404 a, 404 b, a second pairof screw members 406 a, 406 b, a first drive shaft 414 engaging with thefirst pair of screw members 404 a, 404 b, and a second drive shaft 416engaging with the second pair of screw members 406 a, 406 b.

The housing 402 includes a first or bottom shell member 422 and a secondor top shell member 424. The bottom shell member 422 may include aplurality of individual riser members 432 (FIG. 23). The top shellmember 424 may include a plurality of individual riser members 434 (FIG.23). The plurality of individual riser members 432, 434 of the bottomand top shell members 422, 424 may define a first step tracking run 436along a first lateral area 403 of the housing 402 and a second steptracking run 438 along a second lateral area 405 of the housing 402(FIG. 22). The height of the plurality of individual riser members 432,434 may change along the first and second step tracking runs 436, 438.For example, the height of the plurality of individual riser members432, 434 of each of the first and second step tracking runs 436, 438 mayincrease from a central portion 440 of the step tracking extendingdistally from the central portion. The first and second pairs of screwmembers 404 a, 404 b, 406 a, 406 b may each comprise an external helicalthread having a thickness configured to fit in the gaps between adjacentindividual riser members (FIGS. 25-26), to be described in greaterdetail below.

The first drive shaft 414 is operable to rotate the first pair of screwmembers 404 a, 404 b, causing the first pairs of screw members 404 a,404 b to move on the individual riser members 432, 434 defining thefirst step tracking run 436. The second drive shaft 416 is operable torotate the second pair of screw members 406 a, 406 b, causing the secondpair of screw members 406 a, 406 b to move on the individual risermembers 432, 434 defining the second step tracking run 438. In responseto the rotation of the first and second pairs of screw members 404 a,404 b, 406 a, 406 b, the bottom and top shell members 422, 424 may moverelative to each other, effecting an expansion of the housing 402 or acontraction of the housing 402 from the expansion by reversing therotation of the first and/or second pairs of screw members. The firstand second drive shafts 414, 416 may be operable independently of eachother. Therefore, the degree of expansion or contraction of the firstlateral area 403 of the housing 402 is independently adjustable relativeto the degree of expansion or contraction of the second lateral area 405of the housing 402 when the first and second sets of screw members 404a, 404 b, 406 a, 406 b are rotated independently to different positionson the first and second step tracking runs 436, 438.

The positions of the plurality of individual riser members 432 on thebottom shell member 422 may arrange to offset from the positions of theplurality of individual riser members 434 on the top shell member 424 sothat the plurality of individual riser members 432 of the bottom shellmember 422 may intermesh the plurality of individual riser members 434of the top shell member 424 when the housing 402 is in a contractionconfiguration.

The first and second pairs of the screw members 404 a, 404 b, 406 a, 406b may each have a tapered configuration and comprise an external helicalthread, as will be described in greater detail below in connection withFIGS. 25-26. The first pair of screw members 404 a, 404 b may bearranged or disposed such that the directional orientation of theexternal helical thread of the first screw member 404 a of the firstpair is opposite to the directional orientation of the second screwmember 404 b of the first pair so that the first and second screwmembers 404 a, 404 b of the first pair move in an opposite direction inthe first step tracking run 436 relative to each other upon rotation ofthe first drive shaft 414. Similarly, the second pair of screw members406 a, 406 b may be arranged or disposed such that the directionalorientation of the external helical thread of the first screw member 406a of the second pair is opposite to the directional orientation of theexternal helical thread of the second screw member 406 b of the secondpair so that the first and second screw members 406 a, 406 b of thesecond pair move in an opposite direction in the second step trackingrun 438 relative to each other upon rotation of the second drive shaft416.

By way of example, the first and second pairs of screw members 404 a,404 b, 406 a, 406 b may be arranged such that when the first drive shaft414 is rotated in a first direction, e.g. clockwise, the first pair ofscrew members 404 a, 404 b move distally from the central portion 440respectively along the first step tracking run 436, and when the seconddrive shaft 416 is rotated in a second direction opposite to the firstdirection, e.g. counterclockwise, the second pair of screw members 406a, 406 b move distally from the central portion 440 respectively alongthe second step tracking run 438.

Alternatively, the first and second pairs of screw members 404 a, 404 b,406 a, 406 b may be arranged such that when the first drive shaft 414 isrotated in a first direction the first pair of screw members 404 a, 404b move distally from the central portion 440 respectively along thefirst step tracking run 436, and when the second drive shaft 416 isrotated in a second direction same as the first direction the secondpair of screw members 406 a, 406 b move distally from the centralportion 440 respectively along the second step tracking run 438.

Screw Member with Variable Root Radius and Thread Thickness

In some embodiments, the first and second pair of screw members 404 a,404 b, 406 a, 406 b may be tapered screw members having a variable pitchor root radius and an external helical thread with a variable thickness.The variable root radius and thread thickness of the screw members cancreate a tighter fit between the screw members and the individual risersof the shell members, which in turn reduces, minimizes, or eliminatesunwanted micro-motion between parts when the implant device is in itsstarting position, expanded position or lordotically adjusted position.The variable root radius and thread thickness of the screw members alsoallow for a more efficient overall operation mechanism when the screwmembers are moving e.g. climbing up on the individual risers ofincreasing height. These features allow for a smoother motion and moremechanical efficiency during the expansion, contraction, and lordoticadjustment of the implant device.

FIG. 25 shows an exemplary screw member 450 which can be used as one ofthe first and second pairs of screw members 404 a, 404 b, 406 a, 406 baccording to embodiments of the disclosure. As shown, the screw member450 includes an external helical thread 452 winding from a first endsurface 454 to a second end surface 456 of the screw member 450. Thescrew member 450 may be tapered, e.g., having a root radius at the firstend surface 454 different from a root radius at the second end surface456. As used herein, the term “root radius” refers to a dimension of thescrew member 450 measured from the central axis 455 of the screw member450 perpendicularly to the root surface 458 of the screw member 450.

According to embodiments of the disclosure, the screw member 450 mayhave a variable root radius at an end surface or at both end surfaces ofthe screw member 450. As shown in FIG. 25, at the first end surface 454the screw member 450 may have a first root radius R₁ and a second rootradius R₂ where R₁ and R₂ differ, e.g. R₁ is greater than R₂ as shown.At the second end surface 456, the screw member 450 may have a firstroot radius r₁ and a second root radius r₂ where r₁ and r₂ differ, e.g.r₁ is less than r₂ as shown. In some embodiments, a root radius of thescrew member 450 may be ever-changing or change continuously from thefirst end surface 454 to the second end surface 456. For example, asshown in FIG. 25, the change of the root radius from R₁ to r₁ may becontinuous from the first end surface 454 to the second end surface 456of the screw member 450, or the change of the root radius from R₂ to r₂may be continuous from the first end surface 454 to the second endsurface 456 of the screw member 450. Variable root radius allows thescrew member 450 to sit on two individual risers of different heightssimultaneously.

According to embodiments of the disclosure, the external thread 452 ofthe screw member 450 may have a variable thickness. As shown in FIG. 25,the external thread 452 may have a first thickness T₁ at the first endsurface 454 and a second thickness T₂ at the second end surface 456where T₁ and T₂ differ, e.g., T₁ is greater than T₂ as shown. Accordingto embodiments of the disclosure, the thickness of at least a portion ofthe thread 452 is ever-changing, or changes continuously or constantly.In some preferred embodiments, the thickness of the entire externalthread 452 may continuously change from the first end surface 454 to thesecond end surface 456.

Referring to FIG. 26, according to embodiments of the disclosure, theside surfaces of the thread of the screw member 450 may be angled. Forexample, as indicated by line 464 in FIG. 26, the side surface 460 ofthe thread of the screw member 450 may be angled, i.e.,non-perpendicular to the root surface 458 of the screw member 450.According to embodiments of the disclosure, a portion of the sidesurfaces of the riser members may also be angled. For example, asindicated by line 466 in FIG. 26, a portion of the side surface of theriser member 434 may be angled or chamfered, i.e., non-perpendicular tothe end surfaces of the riser 434. As shown in FIG. 26, at least aportion of the side surface 462 of the riser 432 is angled. The angledside surfaces of the screw members and/or riser members can make thecontact between the screw members and the riser members at differentpoints simultaneously, allowing for a smooth motion of the screw membersalong the step track runs as torque is applied to the drive shaftscausing the screw members to rotate and travel.

The features of the screw member 450 provided by this disclosure createa tighter fit of the screw member in the gaps of individual risers. Thetighter fit between the screw member and the individual risers allowsthe implant device to keep stabilized once implanted in between thepatient's intervertebral bodies of the spine and eliminate or reduceunwanted micro-motion. This will help to keep the patient's vertebralspace fixed to the position where the doctor set and promote bone fusionin a better manner. The tighter fit between the screw member and theindividual risers also allows for a smooth operation during surgerywhile the surgeon is using a surgical instrument such as an insertertool to expand and/or lordotically adjust the implant once implantdevice is placed in-between the patient's vertebral bodies. It alsoallows for a fluid and strong distraction force during surgery. In caseswhere the patient's vertebral disc space is collapsed, the mechanism canbe used to distract the disc space to restore the correct intervertebraldisc height.

Extension Springs

In some embodiments, an exemplary spinal implant device according tothis disclosure may include one or more extension springs to assure thatthe entire implant device stays together. Extreme coronal or sagittalimbalances may exist in patients, which may apply uneven distribution offorces on the implant device when implanted in the patients. Unevendistribution of forces on the internal mechanism may causedisassociation of the device. Even before being implanted in thepatient, the device may drop, experience vibration or rattling, causingthe device to disassociate.

The extension spring(s) provided in the implant device of the disclosurecan keep the top and bottom shell members together during its fullycontracted state so that in case the device is dropped, experiencesvibration or rattling, all components in the device are still heldtogether.

The extension spring may also work to keep an opposing force on theassembly. The mechanism inside the device may undergo expansion and/orlordotic adjustment once pressure is applied to the top and bottom shellmembers of the device. An equal and opposite force may be needed for themechanism to move efficiently and correctly. The extension springsprovided in the device of this disclosure may create an initial tensionagainst the mechanism, allowing it to expand and/or adjust lordoticallywhen, for example, the patient's vertebral bodies have not made contactwith the device.

The extension springs may also work to keep the end surfaces or tips ofthe individual risers against the root surface and threads of the screwmembers once expansion and/or lordotic adjustment has taken place. Thisassures that the whole assembly of the device stays together in itsexpanded or lordotically adjusted positions.

Referring now to FIGS. 21-24, the implant device 400 may include a firstextension spring 472 coupling the bottom and top shell members 422, 424and a second extension spring 474 coupling the bottom and top shellmembers 422, 424. It should be noted that one or more than two extensionsprings may be provided in the implant device and adequately perform thefunctions. The first extension spring 472 may be coupled to the top andbottom sell members adjacent to the first step tracking run. The secondextension spring 474 may be coupled to the top and bottom shell membersadjacent to the second step tracking run. The extension springs 472, 474may be attached to the top and bottom shell members using any suitablemeans. By way of example, the extension springs 472, 474 may have hooksat both ends of the springs that hook into loops in the bottom and topshell members 422, 424 as shown. The extension springs 472, 474 may alsobe welded to the top and bottom shell members at the ends of the hooks.

In surgical cases where the implant device is inserted into a patienthaving a large intervertebral disc space anatomy, the extension springs472, 474 can provide an opposing force down on the internal mechanism ofthe implant device 400 to allow it to expand or lordotically adjustuntil it has contacted the patient's vertebral bodies. In surgical caseswhere the implant device 400 is inserted into a patient having a highlevel of lordotic, kyphotic, or coronal imbalances, the extensionsprings 472, 474 will work to apply an opposing force through tension tokeep the mechanism of the implant in contact with itself. This willallow the doctor to place the implant in between these imbalanced discspaces and allow the surgeon to help correct the disc spaces back to anormal sagittal and coronal balance.

Bearing Snap Fit and Graft Ramp

Returning to FIGS. 21-24, in some preferred embodiments, the spinalimplant device 400 may include at least one thrust bearing 480configured to limit axial and/or lateral movement of the drive shafts414, 416 while allowing the drive shafts to rotate or spin about thelongitudinal axes of the drive shafts. The thrust bearing 480 may bedesigned to have a ramp-like geometry 486 that allows an instrumentcarrying a bone graft material to be guided into the implant housing402. This device feature allows for a more efficient surgical instrumentinterface with the implant device, ultimately making the surgery moreefficient.

FIG. 27 is an exploded view of an exemplary thrust bearing 480 accordingto embodiments of the disclosure. As shown, the thrust bearing 480 mayhave a yoke-like configuration comprising a first or top part 482 and asecond or bottom part 484. When connected, the top and bottom parts 482,484 of the thrust bearing 480 define a pair of openings or bearing sitesfor receiving or locking the pair of drive shafts 414, 416 e.g. at theend portions of the drive shafts.

The top and bottom parts 482, 484 of the thrust bearing 480 may beconnected by snap-fit or press-fit through features provided on the topand bottom parts respectively. For example, as shown in FIGS. 27-29, thebottom part 484 of the thrust bearing 480 may include protrusions orguides 486 shaped and sized to be received in corresponding recesses 488in the top part 482 of the bearing 480 by interference fit. In somepreferred embodiments, the snap-fit features in the top and bottom parts482, 484 of the bearing 480 may be configured such that when the top andbottom parts 482, 484 are connected, a portion of the bottom part 484overlaps with a portion of the top part 482, allowing the top and bottomparts 482, 484 to be more “hooked” or connected, as better shown in FIG.24.

Referring to FIG. 29, the drive shafts 414, 416 may each have a roundedportion 415 of a diameter less than the squared or remaining portion ofthe drive shaft. The top and bottom parts 482, 484 of the thrust bearing480 may be configured or sized such that when the top and bottom parts482, 484 are connected, the rounded portions 415 of the drive shafts414, 416 are received in the openings or bearing sites of thrust bearing480, thereby preventing the drive shafts 414, 416 from moving axially orlaterally while allowing the drive shafts 414, 416 to spin or rotateabout their longitudinal axes. In some embodiments, the drive shafts414, 416 may each be provided with an annular ridge 417 in the roundedportion 415. The top and bottom parts 482, 484 of the thrust bearing 480may each be provided with a groove 483, 485 (better shown in FIGS. 27and 28) so that when the top and bottom parts 482, 484 are connected ajournal of the bearing is formed. The annular ridge 417 on the driveshaft may be received in the grooves 483, 485 of the bearing 480,providing an improved engagement of the draft shaft with the thrustbearing. The implant device 400 may include at least one or preferablytwo thrust bearings 480 at an end portion or both end portions of thedrive shafts.

Still referring to FIGS. 27-29, the top part 482 of the bearing 480 mayinclude a “ramp-like” geometry or flat section 486 between the twocurved end sections. This ramp-like section 486, in conjunction with thetop shell 424 of the housing 402, provides an easy access for a surgicalinstrument carrying a bone graft material to be guided into the housingof the implant device 400, as better shown in FIG. 21.

Still referring to FIGS. 27-29, in some embodiments, the thrust bearing480 may be configured to accommodate certain variance of the driveshafts 414, 416 in the operation of the implant device 400. For example,when the implant device 400 is in a parallel configuration as shown inFIG. 30, the drive shafts 414, 416 are closer. When the implant device40 is in a lordosis configuration as shown in FIG. 31, the drive shafts414, 416 are farther apart from each other. The bearing openings may beconfigured to be “slotted” rather than being perfectly circular toaccommodate the variance, as shown in FIGS. 30-31.

Various embodiments of an expandable and adjustable Lordosis interbodyfusion device have been described. It is to be understood that thedisclosure is not limited to the particular embodiments described. Anaspect described in conjunction with a particular embodiment is notnecessarily limited to that embodiment and can be practiced in any otherembodiments.

Various embodiments are described with reference to the figures. Itshould be noted that some figures are not necessarily drawn to scale.The figures are only intended to facilitate the description of specificembodiments and are not intended as an exhaustive description or as alimitation on the scope of the disclosure. Further, in the figures anddescription, specific details may be set forth in order to provide athorough understanding of the disclosure. It will be apparent to one ofordinary skill in the art that some of these specific details may not beemployed to practice embodiments of the disclosure. In other instances,well known components may not be shown or described in detail in orderto avoid unnecessarily obscuring embodiments of the disclosure.

All technical and scientific terms used herein have the meaning ascommonly understood by one of ordinary skill in the art unlessspecifically defined otherwise. As used in the description and appendedclaims, the singular forms of “a,” “an,” and “the” include pluralreferences unless the context clearly dictates otherwise. The term “or”refers to a nonexclusive “or” unless the context clearly dictatesotherwise.

Those skilled in the art will appreciate that various othermodifications may be made. All these or other variations andmodifications are contemplated by the inventors and within the scope ofthe invention.

The invention claimed is:
 1. A device for placement between vertebralbodies, the device comprising: a housing; at least one screw member inthe housing; and at least one drive shaft operably engageable with theat least one screw member, wherein the housing comprises a first shellmember and a second shell member, at least the first shell member havingstep tracking comprising a plurality of individual riser members forreceiving the at least one screw member, the plurality of individualriser members extending a height from an inner surface of the firstshell member, the height of the plurality of individual riser memberschanging along the step tracking, the drive shaft is operable to rotatethe at least one screw member causing the at least one screw member tomove on the plurality of individual riser members, and the at least onescrew member comprises an external helical thread having a thicknessconfigured to fit in a gap between adjacent individual riser members,and a root surface engageable with the plurality of individual risermembers wherein when the root surface of the at least one screw memberis in contact with at least one of the plurality of individual risermembers, a peak of the external helical thread of the at least one screwmember is spaced from the inner surface of the first shell member, andthe first and second shell members move relative to each other inresponse to rotation of the at least one screw member to effect anexpansion of the housing or a contraction of the housing from theexpansion by reversing the rotation of the at least one screw member. 2.The device of claim 1, wherein at least a portion of the externalhelical thread has a continuously changing thickness.
 3. The device ofclaim 1, wherein the plurality of individual riser members have angledside surfaces configured to engage with the external helical thread. 4.The device of claim 1, wherein the at least one screw member comprises avariable root radius.
 5. The device of claim 4, wherein the at least onescrew member is tapered from a first end surface to a second end surfaceand comprises a continuously changing root radius from the first endsurface to the second end surface of the at least one screw member. 6.The device of claim 5, wherein the external helical thread of the atleast one screw member has a continuously changing thickness from thefirst end surface to the second end surface.
 7. The device of claim 6,further comprising at least one extension spring coupled to the firstand the second shell members holding the first and second shell memberstogether at a starting height and/or during expansion and/or contractionof the housing.
 8. The device of claim 1, further comprising at leastone extension spring coupled to the first and the second shell membersholding the first and second shell members together at a starting heightand/or during expansion and/or contraction of the housing.
 9. The deviceof claim 1, wherein the plurality of individual riser members arearranged successively along the step tracking in two series forming atravel pathway for the at least one screw member, wherein riser membersin one of the two series are spaced apart from riser members in anotherone of the two series.
 10. A device for placement between vertebralbodies, the device comprising: a housing; a first set of screw membersand a second set of screw members in the housing; a first drive shaftoperably engageable with the first set of screw members and a seconddrive shaft operably engageable with the second set of screw members,wherein the housing comprises a first shell member and a second shellmember each having a plurality of individual riser members, theplurality of individual riser members of the first and second shellmembers extending a height from an inner surface of the first and secondshell members respectively, wherein the plurality of individual risermembers of the first and second shell members defining a first steptracking run along a first lateral area of the housing and a second steptracking run along a second lateral area of the housing, the height ofthe plurality of individual riser members changing along the first andsecond step tracking runs, the first drive shaft is operable to rotatethe first set of screw members causing the first set of screw members tomove along the first step tracking run, the second drive shaft isoperable to rotate the second set of screw members causing the secondset of screw members to move along the second step tracking run, thefirst and second drive shafts being operable independently of eachother, the first and second sets of screw members each comprises anexternal helical thread having a thickness configured to fit in a gapbetween adjacent individual riser members, and a root surface engageablewith the plurality of individual riser members of the first and secondshell members respectively, wherein when the root surface of at leastone of the first and second sets of screw members is in contact with atleast one of the plurality of individual riser members of the first andsecond shell members, a peak of the external helical thread of the atleast one of the first and second sets of screw members is spaced fromthe inner surface of the first or second shell member, and the first andsecond shell members move relative to each other in response to rotationof the first and/or second sets of screw members to effect an expansionof the housing or a contraction of the housing from the expansion byreversing the rotation of the first and/or second sets of screw members,wherein a degree of expansion or contraction of the first lateral areaof the housing is independently adjustable relative to a degree ofexpansion or contraction of the second lateral area of the housing whenthe first and second sets of screw members are rotated independently todifferent positions on the first and second step tracking runs.
 11. Thedevice of claim 10, wherein the external helical thread of each of thefirst and second sets of screw members has a continuously changingthickness.
 12. The device of claim 10, wherein the plurality ofindividual riser members have an angled side surfaces configured toengage with the external helical thread of each of the first and secondsets of screw members.
 13. The device of claim 10, wherein each of thefirst and second sets of screw members comprises a variable root radius.14. The device of claim 10, wherein each of the first and second sets ofscrew members is tapered from a first end surface to a second endsurface and comprises a continuously changing root radius from the firstend surface to the second end surface.
 15. The device of claim 14,wherein the external helical thread of each of the first and second setsof screw members has a continuously changing thickness from the firstend surface to the second end surface.
 16. The device of claim 15,further comprising at least one extension spring coupled to the firstand the second shell members holding the first and second shell memberstogether at a starting height and/or during adjustment and/or duringexpansion and/or contraction of the housing.
 17. The device of claim 10,further comprising at least one extension spring coupled to the firstand the second shell members holding the first and second shell memberstogether at a starting height and/or during lordosis adjustment and/orduring expansion and/or contraction of the housing.
 18. The device ofclaim 10, further comprising at least one thrust bearing configured toprevent axial and/or lateral movement of the first and second driveshafts, wherein the thrust bearing comprises a first part and a secondpart configured to snap fit together providing a first bearing siteengaging the first drive shaft and a second bearing site engaging thesecond drive shaft.
 19. The device of claim 18, wherein the second partof the thrust bearing member comprises a middle section between thefirst and second bearing sites, wherein the middle section has a rampgeometry allowing an instrument carrying a graft material to be guidedinto the housing.
 20. The device of claim 18, wherein the first andsecond bearing sites of the at least one thrust bearing are configuredto provide openings that are slotted to accommodate variance in spacebetween the first and second drive shafts depending on the degree ofindependent adjustment made to the first lateral area relative to thesecond lateral area.
 21. The device of claim 10, wherein the pluralityof individual riser members of the first and second shell members arearranged successively along the first and second step tracking runsrespectively in two series respectively, forming a first travel pathwayfor the first set of screw members and a second travel pathway for thesecond set of screw members respectively, wherein riser members in oneof the two series of the first travel pathway are spaced apart fromriser members in another one of the two series of the first travelpathway, and riser members in one of the two series of the second travelpathway are spaced apart from riser members in another one of the twoseries of the second travel pathway.